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We present results from a deep Chandra observation of MS1137.5+66, a distant (z=0.783) and massive cluster of galaxies. Only a few similarly massive clusters are currently known at such high redshifts; accordingly, this observation provides much-needed information on the dynamical state of these rare systems. The cluster appears both regular and symmetric in the X-ray image. However, our analysis of the spectral and spatial X-ray data in conjunction with interferometric Sunyaev-Zel'dovich effect data and published deep optical imaging suggests the cluster has a fairly complex structure. The angular diameter distance we calculate from the Chandra and Sunyaev-Zel'dovich effect data assuming an isothermal, spherically symmetric cluster implies a low value for the Hubble constant for which we explore possible explanations., Comment: 16 pages, 6 figures, submitted to ApJ

The mirrors flown in the Chandra Observatory are, without doubt, some of the most exquisite optics ever flown on a space mission. Their angular resolution is matched by no other X-ray observatory, existing or planned. The promise of that performance, along with a goal of achieving 1% calibration of the optics' characteristics, led to a decision early in the construction and assembly phase of the mission to develop an accurate and detailed model of the optics and their support structure. This model has served in both engineering and scientific capacities; as a cross-check of the design and a predictor of scientific performance; as a driver of the ground calibration effort; and as a diagnostic of the as-built performance. Finally, it serves, directly and indirectly, as the primary vehicle with which Chandra observers interpret the contribution of the optics' characteristics to their data. We present the underlying concepts in the model, as well the mechanical, engineering and metrology inputs. We discuss its use during ground calibration and as a characterization of on-orbit performance. Finally, we present measures of the model's accuracy, where further improvements may be made, and its applicability to other missions.

Chandra X-ray Observatory (CXO) the third of NASAs Great Observatories has now been successfullyoperated for four years and has brought us fruitful scienti“c results with many exciting discoveries. The majorachievement comparing to previous X-ray missions lies in the heart of the CXO the High Resolution MirrorAssembly. Its unprecedented spatial resolution and well calibrated performing characteristics are the keys for itssuccess. We discuss the eective area of the CXO mirrors, based on the ground calibration measurements madeat the X-Ray Calibration Facility in Marshall Space Flight Center before launch. We present the derivations ofboth on-axis and o-axis eective areas, which are currently used by Chandra observers.Keywords: Chandra X-ray Observatory, HRMA, X-ray telescopes, X-ray mirrors, calibration, eective area 1. INTRODUCTION NASAs Chandra X-ray Observatory (CXO) is the most powerful X-ray telescope ever built to-date. Its launchin 1999 was a major milestone in the “eld of high energy astrophysics and the world of science. In the past fouryears, it has brought many new discoveries to the general public as well as the scienti“c community, and openeda new window to part of the Universe of which we have never seen before. CXO has unprecedented capabilitiesof high resolution imaging and spectroscopy over the X-ray band of 0.1 keV 10 keV. The success of CXO ismainly due to the design and manufacture of its X-ray mirrors the High Resolution Mirror Assembly (HRMA).At 0.84-m long and 0.6 1.2-m in diameters, the surface area of each mirror ranging from 1.6 to 3.2 squaremeters. They are the largest and the most precise grazing incidence optics ever built. The success of CXO is alsodue to the extensive ground calibration for the HRMA and science instruments, carried out at NASAs MarshallSpace Flight Center before launch. The Eective Area (EA) is one of the most important characteristics of theCXO. It was determined that the CXO eective area should be calibrated to a precision that no X-ray telescopeshave ever achieved before, so it can provide accurate measurement of the ”ux from X-ray sources.

This paper presents a method for modeling the X-ray scattering from random rough surfaces. An actual rough surface is (incompletely) described by its Power Spectral Density (PSD). For a given PSD, model surfaces with the same roughness as the actual surface are constructed by preserving the PSD amplitudes and assigning a random phase to each spectral component. Rays representing the incident wave are reflected from the model surface and projected onto a flat plane, which approximates the model surface, as outgoing rays and corrected for phase delays. The projected outgoing rays are then corrected for wave densities and redistributed onto an uniform grid where the model surface is constructed. The scattering is then calculated by taking the Fast Fourier Transform (FFT) of the resulting distribution. This method is generally applicable and is not limited to small scattering angles. It provides the correct asymmetrical scattering profile for grazing incident radiation. We apply this method to the mirrors of the Chandra X-ray Observatory and show the results. We also expect this method to be useful for other X-ray telescope missions.

One of the major technological challenges for the Constellation X-ray Mission is the development of light-weight, high-resolution, grazing-incidence optics. NASA's Marshall Space Flight Center is developing and evaluating candidate technologies, based upon full-shell replication off precision mandrels. Here we report on recent progress in meeting the weight and imaging-performance requirements, using very thin, high-strength electroformed nickel alloys. In addition, we briefly describe MSFC's optics fabrication, metrology, and x-ray test facilities.

Prior to launch, the High Resolution Mirror Assembly (HRMA) of the Chandra X-ray Observatory underwent extensive ground testing at the X-ray Calibration Facility (XRCF) at the Marshall Space Flight Center in Huntsville. Observations made during the post-launch Orbital Activation and Calibration period, allow the on-orbit condition of the X-ray optics to be assessed. Based on these ground-based and on-orbit data, we examine the alignment of the x-ray optics based on the PSF, and the boresight and alignment of the optical axis alignment relative to the detectors. We examine the vignetting and the single reflection ghost suppression properties of the telescope. Slight imperfections in alignment lead to a small azimuthal dependence of the off-axis area; the morphology of off-axis images also shows an additional small azimuthal dependence varying as 1/2 the off-axis azimuth angle.

The Chandra X-ray Observatory was launched in July 1999, and is returning exquisite sub-arcsecond x-ray images of star groups, supernova remnants, galaxies, quasars, and clusters of galaxies. In addition to being the premier X-ray observatory in terms of angular and spectral resolution, Chandra is the best calibrated X-ray facility ever flown. We discuss here the calibration of the effective area of the High Resolution Mirror Assembly. Because we do not know the absolute X-ray flux density of any celestial source, this must be based primarily on ground measurements and on modeling. In particular, we must remove the calibrated modeled responses of the detectors and gratings to obtain the mirror area. For celestial sources which may be assumed to have smoothly varying spectra, such as the Crab Nebula, we may verify the continuity of the area calibration as a function of energy. This is of significance in energy regions such as the Ir M-edges, or near the critical grazing angle cutoff of the various mirror shells.

The recently launched Chandra x-ray Observatory (CXO) was designed to have the sharpest angular resolution yet of any x-ray telescope. Detailed modeling and metrology of the optics followed by extensive testing at the X-ray Calibration Facility at the Marshall p Space Flight Center in Huntsville, Alabama, indicated that the optics were performing exceedingly well, within our ability to account for distortion of the mirrors due to gravity, and the effects of finite distance and size of the x-ray generator. Thus it was only on-orbit that we expected to directly observe the specified half arcsecond performance. We present here results of the on-orbit calibration of the point spread function (PSF), comparing it with our predictions. We discuss how the PSF varies with source location in the telescope field of view, as well as with the spectral energy distribution of the source.

The Constellation-X Spectroscopy X-ray Telescope (SXT) will provide high-throughput, high-resolution spectroscopy of cosmic sources, from 0.25 keV to 10 keV. Key to this capability is the development of large (1.6 m diameter), lightweight optics for the SXT mirror assembly. Teams led by NASA's Marshall Space Flight Center (MSFC), by NASA's Goddard Space Flight Center (GSFC), and by Italy's Osservatorio Astronomico di Brera (OAB) are currently developing competing mirror technologies for this planned mission. Each team is making significant research progress in developing mirror technologies which satisfy the SXT requirements for lightweight optics, consistent with a system-level optical performance of better than 15 arcsec half-power diameter. The NASA Marshall Space Flight Center (MSFC), in collaboration with the Smithsonian Astrophysical Observatory (SAO), has focussed its efforts on full-shell replicated optics, of electroformed nickel alloys. Recent progress in identifying a surface treatment to effect low, controlled adhesion and, more significantly, in developing new high-strength nickel alloys make this a viable, low cost approach to satisfying the SXT requirements.

The AXAF X-ray mirrors underwent thorough calibration using the X-ray Calibration Facility (XRCF) at the Marshall Space Flight Center in Huntsville, AL from late 1996 to early 1997. The x-ray calibration made novel use of the x-ray continuum from a conventional electron-impact source. Taking advantage of the good spectral resolution of solid-state detectors, continuum measurements proved advantageous in calibration the effective area of AXAF's High-Resolution Mirror Assembly (HRMA) for the entire AXAF energy band. The measurements were made by comparing the spectrum detected by a SSD at the focal plane with the spectrum detected by a beam normalization SSD. The HRMA effective area was calibrated by comparing the measurements with the HRMA raytrace model. The HRMA on-orbit performance predictions are made using the calibration results.

We discuss the x-ray measurement of the focus and alignment of the AXAF (Advanced X-ray Astrophysics Facility) x-ray optics. The high resolution mirror assembly (HRMA) consists of four nested Wolter type I x-ray optics. The attainment of the program goals for high resolution imaging requires that the mirror foci be coincident, both axially and laterally; in addition, the relative tilts between optics within each mirror pair must be small. The mirror tilts and the parfocalization were measured at the X-Ray Calibration Facility (XRCF) at the Marshall Space Flight Center in Huntsville, Alabama during a series of tests in the winter/spring of 1996/1997. The x-ray measurements are compared to the optical alignment data obtained by Eastman Kodak using the HRMA Alignment and Test System (HATS) during HRMA assembly. From these data a preliminary model for the relative location and rigid-body orientation of the individual mirror elements is developed; this mirror model is a component of the SAO high fidelity HRMA raytrace model.

The prelaunch calibration of AXAF encompasses many aspects of the telescope. In principle, all that is needed is the complete point response function. This is, however, a function of energy, off-axis angle of the source, and operating mode of the facility. No single measurement would yield the entire result. Also, any calibration made prior to launch will be affected by changes in conditions after launch, such as the change from one g to zero g. The reflectivity of the mirror and perhaps even the detectors can change as well, for example by addition or removal of small amounts of material deposited on their surfaces. In this paper, we give a broad view of the issues in performing such a calibration, and discuss how they are being addressed in prelaunch preparation of AXAF. As our title indicates, we concentrate here on the total throughput of the observatory. This can be thought of as the integral of the point response function, i.e. the encircled energy, out to the largest practical solid angle for an observation. Since there is no standard x-ray source in the sky whose flux is well known to the approximately 1% accuracy we are trying to achieve, we must do this calibration on the ground. We also must provide a means for monitoring any possible changes in this calibration from prelaunch until on-orbit operation can transfer the calibration to a celestial x-ray source whose emission is stable. In the paper, we analyze the elements of the absolute throughput calibration, which we call the effective area. We review the requirements for calibrations of components or subsystems of the AXAF facility, including the mirror, detectors, and gratings. We show how it is necessary to have an absolute calibrated detection system available during the prelaunch calibrations to measure the flux in the x-ray beam used for calibrating AXAF. We show how it is necessary to calibrate this ground-based detection system at standard man-made x-ray sources, such as electron storage rings. We present the status of all these calibrations, with indications of the measurements remaining to be done, even though the measurements on the AXAF flight optics and detectors will have been completed by the time this paper is presented. We evaluate progress toward the goal of making 1% measurements of the absolute x-ray flux from astrophysical sources, so that comparisons can be made with their emission at other wavelengths, in support of observations such as the Sunyaev-Zeldovitch effect, which can give absolute distance measurements independent of the traditional distance measuring techniques in astronomy.

We discuss the ring focus measurements for the Advanced X-ray Astrophysics Facility (AXAF) x-ray optics -- the high resolution mirror assembly (HRMA). The HRMA is an assembly of four pairs of nested Wolter Type-I grazing incidence mirrors coated with iridium (Ir). The ring focus measurements are an essential part of the AXAF ground calibration carried out at the X-Ray Calibration Facility (XRCF) at the Marshall Space Flight Center (MSFC) in Huntsville, Alabama. The ring focus measurements reveal aspects of the test system distortions and the mirror surface figures which are difficult or impossible to detect in the focal plane. The measurement results show periodic modulations of the ring width which was caused by gravity and strain in the epoxy bonds that are part of the mechanical support system. The strongest component of the modulation has 12-fold symmetry due to the 12 flexures that support each mirror shell. We discuss the ring focus model and compare it with the test results to understand the test system distortions an the mirror glass imperfection, and to predict the impact for the AXAF mirror on-orbit performance.© (1997) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The High Throughput X-ray Spectroscopy (HTXS) mission is dedicated to observations at high spectral resolution. The HXTS mission represented a major advanced, providing as much as a factor of 100 increase in sensitivity over currently planned high resolution X-ray spectroscopy missions. This X- ray equivalent of the Keck Telescope will mark the start of a new era when high quality X-ray spectral will be obtained for all classes of X-ray sources, over a wide range of luminosity and distance. With its increased capabilities, HTXS will address many fundamental astrophysics questions such as the origin and distribution of the elements from carbon to zinc, the formation and evolution of clusters of galaxies, the validity of general relativity in the strong gravity limit, the evolution of supermassive black holes in active galactic nuclei, the details of supernova explosions and their aftermath, and the mechanisms involved in the heating of stellar coronae and driving of stellar winds.

The iridium coating of the AXAF flight optics by Optical Coating Laboratories, Inc. (OCLI) has taken place over the past eight months. During the coating effort, it was necessary to verify the performance of the coatings continually as deposition parameters were changed to accommodate the different geometry of each optic. In addition, quick look reflectivity measurements have been completed for witness samples coated during each run. The minimum reflectivity to be met was 82 percent at 20 arcminutes grazing angle and 50 percent at 34 arcminutes grazing angle. THis can be compared with a theoretical reflectivity, based on the Henke coefficients, of 88 percent and 62 percent at 20 and 34 arcmin respectively. Previous measurements by P. Slane, et al., gave mean values of 84 percent at 20 arcmin and 51 percent at 34 arcmin grazing angle. Measurements reported here were carried out by the SAO reflectivity laboratory, which is part of the AXAF mission support team. The quick look results of both the qualification samples and the production samples are presented along with the test results from the scaleup and verification runs that were used to set the coating parameters.

The Mission Support Team SAO Reflectivities studies laboratory was responsible for the verification of the coating performance specification during the coating of the eight AXAF flight optics. Prior to the start of the coating of the flight optics, it was necessary to verify the scaleup of the coating chamber parameters from the test chamber to the flight optic coating chamber as well as to verify repeatability of coating quality. Immediately prior to the coating of each flight optic, witness samples were coated to verify the coating specification for each particular geometry. Similar witness samples were coated to verify the coating specification for each particular geometry. Similar witness samples were also coated with each flight optic. An overview of this monitoring program is presented along with a description of how the measurements are made, what tests are used to verify performance and a description of the witness sample deployment. Preliminary data on coating uniformity will also be presented.

One of the specifications used to polish the AXAF witness samples was that the rms surface roughness be

The AXAF VETA-I mirror x-ray test results have been cross checked with predictions based upon the HDOS metrology measurements and calculations of the effects of imperfect test system geometry and mirror mount induced distortions. The cross check was done by comparing the VETA-I x-ray test results with a VETA-I model, which is a computer simulation of the VETA-I mirror performance during the x-ray test. The HDOS (Hughes Danbury Optical Systems, Inc., Danbury, Conn.) metrology measurements (with CIDS, PMS, and WYKO) were performed after the VETA-I x-ray test in order to determine the surface figure errors of the mirror pair, including the overall surface map and the surface roughness. Mirror performance was predicted based on the measured surface figure errors and x-ray scattering theory. All the VETA-I x-ray test data (FWHM, encircled energy, effective area, wing scan, and ring focus) were cross checked with the HDOS metrology measurements. The results of this study show reasonably good agreement between the x-ray test data and the metrology data. Similar analysis should be performed for the HRMA mirrors, which is an important step in securing a scientifically successful AXAF mission.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

The Advanced X-ray Astrophysics Facility (AXAF) is the x-ray component of NASA's Great Observatories. To be launched in late 1998, AXAF will provide unprecedented capabilities for high-resolution imaging, spectrometric imaging, and high-resolution dispersive spectroscopy, over the x-ray band from about 0.1 keV to 10 keV. With these capabilities, AXAF observations will address many of the outstanding questions in astronomy, astrophysics, and cosmology.

Four reflection, grazing incidence X-ray optics offer the possibility of broad band (0.1-10.0 keV) X-ray telescopes that fit within the physical envelope of NASA's Small and Medium Explorer mission. We describe a short focal length (4 m) optical design with arcsec imagery over a 1 degree(s) field of view and good efficiency in the Fe-K band (6.4-7.1 keV).

The downhill simplex and simulated annealing algorithms are powerful design tools for optical systems that do not yield to analytic methods of optimization. Use of these numerical techniques have been frustrated by the shortage of computational resources available to investigators. To tap the latent computational resources available in even moderate sized local area networks (LAN's), we have developed software to operate flexibly, a LAN composed of UNIX workstations as a distributed processor for optical design optimization. We have developed a general purpose remote procedure call generator and subroutine library which allow simple specification and use of existing subprograms as remote procedures. This software provides a mechanism for modifying or developing large scientific and engineering applications with inherent parallelism for distributed processing on LAN's. We discuss the performance, bandwidth, and adaptability of this software as applied to the problem of grazing incidence optics design using the simulated annealing algorithm.

The study measures the X-ray reflectivity of the AXAF VETA-I optic and compares it with theoretical predictions. Measurements made at energies of 0.28, 0.9, 1.5, 2.1, and 2.3 keV are compared with predictions based on ray trace calculations. Results on the variation of the reflectivity with energy as well as the absolute value of the reflectivity are presented. A synchrotron reflectivity measurement with a high-energy resolution over the range 0.26 to 1.8 keV on a flat Zerodur sample is also reported. Evidence is found for contamination of the flat by a thin layer of carbon on the surface, and the possibility of alteration of the surface composition of the VETA-I mirror, perhaps by the polishing technique. The overall agreement between the measured and calculated effective area of VETA-I is between 2.6 and 10 percent. Measurements at individual energies deviate from the best-fitting calculation to 0.3 to 0.8 percent, averaging 0.6 percent at energies below the high energy cutoff of the mirror reflectivity, and are as high as 20.7 percent at the cutoff.

We employ the X-ray measurements of the VETA-I taken at the X-Ray Calibration Facility (XRCF) of the Marshall Space Flight Center (MSFC) to extract information about the surface finish quality of the outermost pair of AXAF mirrors. The particular measurements we consider are 1D scans of the core of the point response function (PRF) (FWHM scans), the encircled energy as a function of radius, and 1D scans of the wings of the PRF. We discuss briefly our raytrace model which incorporates the numerous effects present in the VETA-I test, such as the finite source distance, the size and shape of the X-ray source, the residual gravitational distortions of the optic, the despace of the VETA-I, and particulate contamination. We show how the data constrain the amplitude of mirror surface deviations for spatial frequencies greater than about 0.1/mm. Constraints on the average amplitude of circumferential slope errors are derived as well.

X-ray testing of the AXAF outer mirror pairs, in the VETA-1 configuration, reveals a point spread function (PSF) with unexpectedly large wings at low energies. Although the angular dependence in the wings of the PSF is close to that expected for diffractive scattering from surface roughness, the energy dependence differs substantially. Analyses of the observed X-ray PSF, images near ring focus, and single-quadrant images at conjugate focus suggest that the excess scattering observed at low X-ray energies results from diffractive scattering by relatively small grains (as small as a few tenths micrometer in radius). We develop a simple model for the contribution of scattering by particulates to the PSF. Merging this model with that for scattering by surface roughness, we fit the combined model to the observed energy-dependent PSF, in order to estimate parameters and associated uncertainties characterizing the grain-size distribution and the surface-roughness power spectral density. In particular, we find that the fractional coverage of the mirrors by particulates is approximately 1 x 10 exp -4 (for grain radii between 0.1 and 10 microns), and that the rms surface-roughness is approximately 0.7 nm (for spatial frequencies between 1/mm and 1000/mm).

The energy bandwidth and total throughput of a grazing incidence optics system is a strong function of the X-ray reflectivity of the surface coating. In support of the Advanced X-ray Astrophysics Facility (AXAF), studies are underway to evaluate and characterize the reflectivity of potential AXAF coatings. Here we report on results obtained for Au, Ir, and Ni coatings produced by electron-beam evaporation, evaporation with ion-assist, and sputtering. Effects of coating thickness and deposition angle have been evaluated at 6.4 and 8.1 keV; the highest reflectivities are those of the thinner, about 200 A vs about 700 A, coatings. While considerable variations exist, the best Ir samples have higher reflectivity than any of the Au coatings. Data results have been compared with models for theoretical reflectivity, particularly with regard to the effective density of the coatings. Independent measurements of the coating densities have been carried out for comparison with the reflectivity results.

The recently polished outer AXAF mirror pair soon will be tested at Marshall Space Flight Center's new x-ray facility. The expected performance is discussed.

The authors discuss the optics and instruments of NASA’s nearly completed x-ray observatory.

The quantum efficiency of microchannel plates has been measured at energies from 0.28 to 3.0 keV and at angles less than 6°. The quantum efficiency reaches a maximum of 27% at 3° and an energy of 0.86 keV. At all energies, the quantum efficiency increases as the angle of incidence decreases until a critical angle is reached, after which the efficiency decreases rapidly. The quantum efficiency, outside of the small angle dip, decreases with energy at a constant angle. The general behaviour of the quantum efficiency can be understood using a very simple physical model. The low angle dip is caused by reflection from the surface of the channel. The variation of the quantum efficiency as a function of energy can be explained by the variation of the X-ray absorption and of the photo- and Auger electron ranges. The data are reasonably reproduced by a simple model.

In this talk, I will discuss some of the history and unique aspects of the optics development for HEAO-B, mention some of the results of the program to illustrate its success, and, finally, give some thoughts for future large scientific programs of this type.

Summary not available.

The manufacture and testing of the Technology Mirror Assembly (TMA), a prototype Wolter I telescope scaled to the dimensions of the innermost element of the High-Resolution Mirror Assembly for the NASA Advanced X-ray Astrophysics Facility (AXAF), are reviewed. Consideration is given to the grinding, polishing, coating, and assembly of the zerodur TMA blanks, the TMA mount design, and the test procedures used at the MSFC X-ray Calibration Facility. Test results indicate FWHM resolution less than 0.5 arcsec, but with significant near-field scattering attributed to ripple; further long-lap polishing is suggested.

The fabrication of the Technology Mirror Assembly (TMA) is complete, and performance predictions were made based upon mechanical and visible light measurements of the surface properties. An X-ray calibration program has been executed, and a preliminary analysis of a portion of the data is presented. The X-ray image distribution results are in reasonable agreement with the performance predictions which were calculated prior the start of the X-ray tests. The measured X-ray imaging performance approaches that expected for the Advanced X-ray Astrophysics Facility (AXAF).

The major telescopes in this program are the one flown on the Einstein or HEAO-B satellite in 1978 and the one planned for the AXAF which should be launched in late 1995. The x-ray performance of the Einstein mirror is reviewed briefly, and its surface properties are inferred from a combination of its x-ray properties and the information available from the limited fabrication metrology of that era. The improvements necessary for satisfying the AXAF specification are summarized. Much of this technology already has been demonstrated in the TMA program, and this progress is reviewed.

We have developed a math model relating the measured parameters of the Technology Mirror Assembly (TMA) to its final performance. This scalar scattering model is valid for large and small amplitude features. It allows the user to specify power spectral densities and/or autocovariance functions within any spatial bandwidth, including microroughness. We present new TMA data in the bandwidth of ~0.1-1000 mm(-1), predicting performance and comparing them with x-ray test data. We also account for assembly, alignment. and particulate contamination. Finally, we comment on improved performance expected after repolishing.